On Paper Vs Ballistic Program

I realize numbers in the computer and bullet holes on paper can be way off. Kinda like theory and reality. I am shooting a Remington sendero 300 rum 6.5 x 20 long range Leupold with a gentry brake. I am loading 100.5gr retumbo w/ 180 gr accubond. I have chronographed the load at 3355fps avg. I am shooting 2.8 inches high at 100 for a 300 yard zero. Here is the problem, when I shoot the 300 yd target, I am actually 3.5 in low. My question is how do I dial up to 400 yards or further if the ballistics info is that inaccurate at close range.
I am using the shooting chrony's ballistic program. Any suggestions other than shooting and documenting the poi. at all ranges? I am limited to a 300 yard shooting range. I am new to trying to strech the range but not to shooting out past 300 yad. I just have never had the optics or a flat shooting rifle to do so.
Thanks for the responses,

Shawn

Shawn, I agree with you.
I have three ballistic programs and they all three give me the same results for distances up to 1000+ yards. When using the G1 drag model even when it may not be the proper model, most programs are accurate to 500, 600 yards. In your case, something is not right, for example at sea level with MV=3355, your should zero at 2.4 high at 100 yards to be dead on at 300. At 7000 ft elevation, you would have to zero at 2.2" high at 100 to be dead on at 300. Tht's if your scope hight is 1.8" or so. Therefore your info is not making sence. If at 100 yrds you're 2.8" high, then at 300 you should be 1" high. At sea level that is. Then I would make sense to say: 2.8" hight at 100 and 3.5" low at 368 yards. Now if I play with the muzzle velocity, for example, if MV=2850 f/s, BC=0.507,Elev=0, 2.8" high impact point at 100 yards; now it would be exactly 3.5" low at 300 yards.
I'm lost friend, I don't know what's doing that! In the past I loaded 180 grains accubond using retumbo 100.0 gr. and I was getting high pressures. and velocities way over 3400 f/s; therefore I could not say you are running velocities of 2850 unless your barrel is shot out and your chrony is no good.
What are the chances of that to be so? Probably slim.
Try shooting at 400 yards, if your impact point is close to 16" low then your muzzle velocity would have to be 2850 f/s, that's again assuming you are at sea level and your scope is mounted 1.8" high.
Good luck!

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HEBREWS 13:8

Jesus Christ the same yesterday, and to day, and for ever.

Our Lord Jesus said that as it was in the days of Noah and
also as it was in the days of Lot so it shall be in the days...
It's happening again!!! God sent to us His prophet, and His Word
to this generation and we once more are rejecting it as was prophesied!!! ---> As promised, God Sent His Prophet to us!

In response to Eaglet, the gun was bought new in Nov 06' has about 130-150 rounds down the pipe and the choro in a new gamma master. Since I do not have a 400 yd range, I am going to re zero at 100 and shoot out to 300and measure my drops. Then I can put the numbers into the program and see if the chrony is wrong. First, I have another issue to address as I shot Saturday evening. What a flop ,.. can you say frustrated! I loaded 10 rounds. Cold gun clean barrel. First shot at 300 on a redfield target was 3" low and 4 " left windage. Ok I thought, first shot would be off due to clean barrel with lube residue. Second shot, 3 low 4 left. 15 minutes betweet shots. Ok we have consistancy, but nooooooo the third shot was 4 left and 1 low.. OK I pulled, 4 th was 4 high and 4 left..Thats a 5" difference in the poi. 5th shot was 2 left 2 low. I did not finish the other 5 as I had enough.

In response to Eaglet, the gun was bought new in Nov 06' has about 130-150 rounds down the pipe and the choro in a new gamma master. Since I do not have a 400 yd range, I am going to re zero at 100 and shoot out to 300and measure my drops. Then I can put the numbers into the program and see if the chrony is wrong. First, I have another issue to address as I shot Saturday evening. What a flop ,.. can you say frustrated! I loaded 10 rounds. Cold gun clean barrel. First shot at 300 on a redfield target was 3" low and 4 " left windage. Ok I thought, first shot would be off due to clean barrel with lube residue. Second shot, 3 low 4 left. 15 minutes betweet shots. Ok we have consistancy, but nooooooo the third shot was 4 left and 1 low.. OK I pulled, 4 th was 4 high and 4 left..Thats a 5" difference in the poi. 5th shot was 2 left 2 low. I did not finish the other 5 as I had enough.

If I followed this right, this is how your target looked like:

If we call the one far above a flyer, you do not have such a bad group. You
would have 4 shots in 2.24 inches at 300 yards, which is 0.71 MOA; or about 3/4" group at 100 yards, which in all honesty the rifle shooter combo would have to shoot better than 3/4" at 100 yards to be able to shoot 2.24" at 300 yards. You know, the bullet has to fly 3 times the distance and its exposed in the air for a longer time. Some rifles do need 2 or 3 shots after a clean barrel before they start falling in place. Also, don't forget the swivels in the stock, if they're getting caught
in the process you'll have lots of problems.

__________________

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-----------------------------

HEBREWS 13:8

Jesus Christ the same yesterday, and to day, and for ever.

Our Lord Jesus said that as it was in the days of Noah and
also as it was in the days of Lot so it shall be in the days...
It's happening again!!! God sent to us His prophet, and His Word
to this generation and we once more are rejecting it as was prophesied!!! ---> As promised, God Sent His Prophet to us!

The target is 99% correct. The first shot lower left was 3" left and the second was 4" left. otherwise exactly as described I guess I am expecting the group to be uniform like I get at 100, just to open up a little. So taking all the variables; ie, my shooting skill, wind, distance, temp humidity, elevation ect, my expectations are unreasonable from a production rifle. I still need to rezero at 100 and check the drop at 200 & 300 to see if my chrony is off. I always try to eliminate as many variables as possible and shoot when there is no wind,In the last 2 weeks, he have had very light to no wind at all. ALSO , HOW DO I POST A PHOTO?

The target is 99% correct. The first shot lower left was 3" left and the second was 4" left. otherwise exactly as described I guess I am expecting the group to be uniform like I get at 100, just to open up a little. So taking all the variables; ie, my shooting skill, wind, distance, temp humidity, elevation ect, my expectations are unreasonable from a production rifle. I still need to rezero at 100 and check the drop at 200 & 300 to see if my chrony is off. I always try to eliminate as many variables as possible and shoot when there is no wind,In the last 2 weeks, he have had very light to no wind at all. ALSO , HOW DO I POST A PHOTO?

s.ferg,
Lots of folks expect to get 1/2" groups with hand loads from the Rem. Senderos. I personally believe that if you can get 3/4" @ 100 yards or less you're doing pretty good specially if you haven't had things done like glass bedding the action and doing a trigger job. I had those things done on my 300 RUM Sendero and I even got a torque wrench to insure right torque on the action screws and my rifle will shoot consistant to about 1.6" to 1.9" @ 300 yrds using virgin brass; that's about 0.53 to 0.65 @ 100 yards and I'm very happy with it. I believe it'll get better with once fired brass. Remember some folks are happy with a custom barrel that'll shoot 1.5" @ 300 yards and many expect 1.0" 5 shot groups @ 300 yards. Then again the guns are awesome and the shooters are right there. What you're thinking on doing is a good idea in my opinion. Don't give up!

Shot from prone using a Harris bipod. Not from inside the car...

__________________

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-----------------------------

HEBREWS 13:8

Jesus Christ the same yesterday, and to day, and for ever.

Our Lord Jesus said that as it was in the days of Noah and
also as it was in the days of Lot so it shall be in the days...
It's happening again!!! God sent to us His prophet, and His Word
to this generation and we once more are rejecting it as was prophesied!!! ---> As promised, God Sent His Prophet to us!

I used the ladder method to find the tightest and most consistant at 100 yards. I got this load to shoot a 3 shot group of (I believe) .312.. I have noticed that some of the brass that I am reloading is a tighter when chambered, so I wonder if that has anything to do with my consistancy. I have 200 rounds of new brass that I need to prep and load. In the future, I am going to have the action accurized and a jewell trigger installed. Right now, I just just want to get a happy median to shoot a muley and possibly an elk of it shows it face.